JPH09257001A - Hydraulictransmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform proper compensation of a load in the whole stroke region of a directional switching valve when when an actuator is driven through operation of an open sensor directional switching valve. SOLUTION: A pressure control valve 12 is located in a bypass pipe line 13 situated downstream from the center bypass throttle 11 of a directional switching valve 10 and a pressure producing device 20 is arranged further downstream therefrom. A pressure generated by the pressure producing device 20 is guided to the inclination control device 2n of a hydraulic pump 1 and a delivery flow rate of the hydraulic pump 1 is controlled to a negative flow rate of a hydraulic pump 1 according to a pressure. A control force in an opening direction is exerted on the pressure control valve 12 by the outlet pressure of a center bypass throttle 11. A control force in a closing direction is exerted by the load pressure of an actuator 5, and the outlet pressure of the center bypass throttle 11 is controlled to the same value as the load pressure amount of the actuator 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive system provided in a hydraulic machine such as a hydraulic excavator or a hydraulic crane, and more particularly to an open center having a center bypass throttle on a bypass passage communicating a hydraulic pump and a tank. Hydraulic drive with a directional control valve.

[0002]

2. Description of the Related Art As a prior art of a hydraulic drive system having an open center type directional control valve having a center bypass throttle on a bypass passage communicating a hydraulic pump and a tank, it is disclosed in Japanese Patent Laid-Open No. 6-117409. There is something. This prior art is shown in FIG.

In FIG. 10, an open center type directional control valve 50 is connected to the supply passage 3 for the discharge flow rate from the variable displacement hydraulic pump 1, and the pressure supplied to the actuator 5 by operating the directional control valve 50. The oil flow rate is controlled. Further, in the bypass passage 4 branched from the supply passage 3,
A directional switching valve 50 is provided with a center bypass throttle 51 that interlocks so that the opening area becomes smaller as the stroke (switching amount) of the valve 50 increases, and a bypass conduit downstream of the center bypass throttle 51. 13 is provided with a variable throttle valve 52 and a throttle 21, the pressure generated in the throttle 21 is guided to a tilt control device 2n of the hydraulic pump 1 via a signal line 23, and the discharge flow rate of the hydraulic pump 1 is corresponding to the pressure. The negative flow rate is controlled.

Further, the direction switching valve 50 can detect the downstream pressure of the meter-in throttle, that is, the load pressure of the actuator 5, and the detected pressure is detected via the signal line 53 in the closing direction of the variable throttle valve 52. It has a structure that acts on.

When excavation work is carried out by mounting the hydraulic drive device on a hydraulic excavator as described above, when the direction switching valve 50 is operated by the operation lever device 54, the center bypass throttle 51 is throttled and the bypass flow rate is reduced. Then, the pressure generated in the throttle 21 is reduced, and the discharge flow rate of the hydraulic pump 1 is controlled to increase by the pressure detected in the signal conduit 23. When the discharge pressure of the hydraulic pump 1 becomes higher than the load pressure of the actuator 5, pressure oil starts to be supplied to the actuator 5 via the meter-in throttle of the direction switching valve 50, and the stroke of the direction switching valve 5 (the meter-in throttle is supplied to the actuator 5). The flow rate is supplied according to the opening area).

When the load pressure of the actuator 5 increases in such a state, the discharge pressure of the hydraulic pump 1 starts to increase accordingly, and if the variable throttle valve 52
Is not provided, the pressure generated in the throttle 21 increases due to the increase in the pump discharge pressure, and the discharge flow rate of the hydraulic pump 1 is controlled to decrease. Therefore, even if the stroke of the direction switching valve 50 (the opening area of the meter-in throttle) is constant, the flow rate supplied to the actuator 5 is reduced. Further, since the dead zone is generated on the small stroke area side of the direction switching valve 50, the effective stroke area is narrowed and the operability is deteriorated.

In the above conventional technique, since the variable throttle valve 52 is provided in the bypass line 13, the actuator 5
When the load pressure of the hydraulic pump 1 increases, the load pressure detected in the signal pipe 53 narrows the opening area of the variable throttle valve 52, the bypass flow rate decreases, the pressure generated in the throttle 21 decreases, and The discharge flow rate is controlled to increase. As a result, the discharge pressure of the hydraulic pump 1 further increases without decreasing the discharge flow rate of the hydraulic pump 1, and a load compensation characteristic capable of supplying the same flow rate to the actuator 5 as before the load pressure increases is obtained.

[0008]

However, the above-mentioned conventional hydraulic drive system has the following problems.

First, in the load compensation of the conventional hydraulic drive system described above, the variable throttle valve 52 that throttles the opening area in response to the load pressure is provided in the bypass line 13 as described above. On the other hand, the idea is to add throttle resistance in accordance with the load pressure in addition to the throttle resistance of the center bypass throttle 51, and the method of simply adding throttle resistance in this way is to use the center bypass in the full stroke range of the directional control valve 50. It is not possible to match with the aperture, and appropriate load compensation cannot be performed in the stroke region where no matching is performed.

For example, the variable throttle valve 52 is provided so that a desired meter-in flow rate (flow rate supplied to the actuator 5) can be obtained by the throttle amount (opening area) of the center bypass throttle 51 at a certain point in the first half of the stroke of the direction switching valve 50. When the setting (spring constant and throttle opening amount) is performed, when the variable throttle valve 52 is throttled as the load pressure increases in a stroke region larger than the matching stroke point, this throttle resistance becomes excessive and the bypass flow rate is increased. If it decreases too much, the discharge flow rate of the hydraulic pump 1 unnecessarily increases, and the meter-in flow rate increases remarkably. Therefore, the discharge flow rate of the hydraulic pump 1 saturates at an early stage, and a dead zone, which has never existed in the past, is generated on the maximum side of the stroke, and eventually the effective stroke is reduced and the operability is deteriorated.

In a stroke region larger than the matching stroke point, proper load compensation cannot be performed as described above, and the pump discharge flow rate increases more than necessary, and
Since the throttling resistance of the variable throttle valve 52 becomes excessive, the pump discharge pressure also rises more than necessary, which causes a problem that energy efficiency is lowered.

Further, the hydraulic excavator is provided with a plurality of directional switching valves corresponding to a plurality of actuators, and the opening area of the center bypass throttle 51 built in these plurality of directional switching valves is different for each actuator. Various settings are made. Therefore, even at one of the matching stroke points, the setting of the unique throttle operation of the variable throttle valve 52 provided in the bypass passage 4 makes it possible to compensate the load compensation intended for driving the actuator for all of the plurality of directional control valves. Will be difficult to do.

A first object of the present invention is to provide a hydraulic drive system capable of performing appropriate load compensation in the entire stroke region of a directional control valve when operating an open center type directional control valve to drive an actuator. Is.

A second object of the present invention is to provide an appropriate load compensation when operating an actuator by operating an open center type directional control valve, regardless of the setting of the opening area of the center bypass throttle of the directional control valve. An object of the present invention is to provide a hydraulic drive device that can be easily performed.

[0015]

[Means for Solving the Problems]

(1) In order to achieve the first and second objects, the present invention includes a hydraulic pump, at least one actuator driven by pressure oil discharged from the hydraulic pump, the hydraulic pump and a tank. An open center type directional control valve having a center bypass throttle on a bypass passage communicating with the pump, and pump control means for controlling the discharge flow rate of the hydraulic pump according to the operation of the directional control valve,
In a hydraulic drive device that controls a flow rate of pressure oil supplied from the hydraulic pump to the actuator in accordance with an operation of the direction switching valve, a detection unit that detects a load pressure of the actuator, and the center bypass of the bypass passage. The outlet pressure of the center bypass throttle is applied in the valve opening direction, the load pressure detected by the detection means is applied in the valve closing direction, and the outlet pressure of the center bypass throttle is applied to the actuator. And a pressure control valve that controls the load pressure to be the same.

In the present invention configured as described above,
By controlling the pressure control valve so that the outlet pressure of the center bypass throttle of the directional control valve is the same as the load pressure of the actuator, the differential pressure across the meter-in throttle of the directional control valve and the differential pressure across the center bypass throttle are controlled. The discharge flow rate of the hydraulic pump is almost equal, and the discharge flow rate of the hydraulic pump is always distributed to the actuator inflow flow rate and the bypass flow rate according to the opening area ratio of the meter-in throttle of the direction switching valve and the center bypass throttle. Therefore, if the directional control valve is operated and the meter-in throttle is opened, the flow rate of the ratio corresponding to the opening area ratio is always supplied to the actuator at that time, and the stroke position at which the flow of pressure oil to the actuator starts is determined. It is almost constant regardless of the load pressure. Further, by controlling the discharge flow rate of the hydraulic pump 1 according to the operation of the directional control valve, when the discharge flow rate of the hydraulic pump is distributed according to the opening area ratio, the stroke position of the directional control valve is determined. Also, the flow rate into the actuator becomes a flow rate according to the opening area ratio at that time, and appropriate load compensation can be performed in the entire stroke region of the directional control valve.

Further, since the pressure control valve controls the outlet pressure of the center bypass throttle of the directional control valve to be the same as the load pressure of the actuator, the opening area of the center bypass throttle of the directional control valve is different for each actuator. The same effect can be obtained by using the same pressure control valve even if various settings are made, and proper load compensation can be easily performed regardless of the setting of the opening area of the center bypass throttle.

(2) In order to achieve the above first and second objects, the present invention provides a hydraulic pump, a plurality of actuators driven by pressure oil discharged from the hydraulic pump, and the hydraulic pressure. A plurality of open center type directional control valves, which are connected in series to a bypass passage that communicates the pump and the tank and each have a center bypass throttle on the bypass passage, and the hydraulic pump according to the operation of the plurality of directional control valves. And a pump control means for controlling the discharge flow rate of the hydraulic drive device for controlling the flow rate of the pressure oil supplied from the hydraulic pump to the plurality of actuators according to the operation of the plurality of directional control valves. Detection means for detecting the maximum load pressure of a plurality of actuators, and the downstream side of the most downstream center bypass throttle in the bypass passage Is arranged, the outlet pressure of the restrictor downstream of the center bypass is applied in the opening direction, the maximum load pressure detected by said detecting means is applied in the closing direction,
And a pressure control valve that controls the outlet pressure of the most downstream center bypass throttle so as to be the same as the maximum load pressure.

As described above, in the hydraulic drive system having a plurality of actuators and a plurality of directional control valves, the maximum load pressure is detected and the pressure control valve sets the outlet pressure of the center bypass throttle at the most downstream to the same as the maximum load pressure. By controlling so that, when each actuator is operated independently, the same action as (1) above can be obtained. In addition, if a pressure compensation valve that keeps the differential pressure across the meter-in throttle constant is provided for each of the directional control valves, it is possible to reduce the meter-in throttle of each of the directional control valves during a combined operation that simultaneously drives multiple actuators. The front-rear differential pressure and the upstream and downstream differential pressures of the plurality of center bypass throttles are all substantially equal, and the discharge flow rate of the hydraulic pump depends on the opening area ratio between the meter-in throttle and the center bypass throttle of each of the directional control valves. The flow rate is distributed to the plurality of actuators and the bypass flow rate, and appropriate load compensation can be performed in the entire stroke region of each directional control valve.

(3) In the above (1) or (2), preferably, the hydraulic pump is a variable displacement type, and the pump control means is disposed further downstream of the pressure control valve in the bypass passage, and the bypass is provided. Pressure generating means for generating a pressure according to the flow rate in the passage and tilt control means for controlling the negative displacement of the discharge capacity of the hydraulic pump according to the pressure generated by the pressure generating device.

By providing the tilt control means for controlling the negative displacement of the discharge capacity of the hydraulic pump as described above, the discharge flow rate of the hydraulic pump is the opening area ratio between the meter-in throttle and the center bypass throttle of the directional control valve as described above. When the flow rate is divided into the actuator inflow flow rate and the bypass flow rate according to the above, the bypass flow rate also becomes a flow rate according to the opening area ratio, and even if the load pressure increases, the bypass flow rate does not excessively decrease, and the hydraulic pump 1 Premature saturation of the discharge flow rate is avoided. As a result, regardless of the stroke position of the directional control valve, the flow rate into the actuator becomes a flow rate according to the opening area ratio at that time, and appropriate load compensation can be performed in the entire stroke area of the directional control valve.

(4) Further, preferably, the hydraulic pump is of a variable displacement type, and the pump control means detects the operation signal of the operation means for the directional control valve,
Tilt control means for positively controlling the discharge capacity of the hydraulic pump according to the operation signal detected by the detection means.

Even when the tilt control means for controlling the positive displacement of the discharge capacity of the hydraulic pump is provided as described above, the hydraulic pump can be operated even when the load pressure is increased, as in the case of providing the tilt control means for controlling the negative flow rate. It is possible to prevent the discharge flow rate of No. 1 from saturating at an early stage, and to perform appropriate load compensation in the entire stroke region of the directional control valve.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, reference numeral 1 denotes a variable displacement hydraulic pump, an open center type directional control valve 10 is connected to a supply passage 3 for the discharge flow rate from the hydraulic pump 1, and the directional control valve 10 is an operating lever. When operated by the device 30, the meter-in throttles 10a and 10b built in the direction switching valve 10 are provided.
The opening area of is changed and the flow rate of the pressure oil supplied to the actuator 5 is controlled. Further, in the bypass passage 4 branched from the supply passage 3, there is provided a center bypass throttle 11 which is built in the directional control valve 10 and which interlocks so that the opening area becomes smaller as the stroke (switching amount) of the directional control valve 10 increases. The pressure control valve 1 is provided in the bypass pipe line 13 on the downstream side of the center bypass throttle 11.
2 are provided. Further, a pressure generator 20 including a throttle 21 and a relief valve 22 is provided further downstream of the pressure control valve 12 in the bypass pipe line 13.
The pressure (negative control pressure) generated in 1 is guided to the tilt control device 2n of the hydraulic pump 1 via the signal line 23, and the discharge flow rate of the hydraulic pump 1 is negatively controlled according to the pressure.

As usual, the operating lever device 30 comprises an operating lever 30a and a pair of pressure reducing valves 30b, 30c which operate in accordance with the operating direction and amount of operation of the operating lever 30a. The pilot pressure generated in 30c is guided through the pilot pipe lines 31a and 31b to switch the directional control valve 10.

The direction switching valve 10 includes the direction switching valve 10
The detection paths 14a and 14b guide the downstream pressure of the meter-in throttles 10a and 10b as the load pressure of the actuator 5 in accordance with the switching operation in the illustrated left and right direction, and the drain path 14c which is effective in the illustrated neutral state of the direction switching valve 10. Are provided, and according to the operation of the direction switching valve 10, the detection paths 14a, 14
b and the drain path 14c are connected to the signal pipe 12b.

The pressure control valve 12 includes a valve body 12v, a signal line 12a connected to the upstream side of the pressure control valve, that is, an outlet side of the center bypass throttle 11 of the direction switching valve 10, and the signal line 12b. , The spring 12s, and the outlet pressure of the center bypass throttle 11 is guided to open the valve body 12v via the bypass conduit 13 and the signal conduit 12a,
The control force in the valve opening direction is applied, the load pressure of the actuator 5 is guided to close the valve body 12v via the signal conduit 12b, and the control force in the valve closing direction is applied together with the spring 12s. The spring 12s keeps the valve body 12 in the valve closing position when the hydraulic drive system is not operated, and is set to have a weak spring force.

Reference numeral 6 is a safety valve, and 7 is a check valve.

FIG. 2 shows the relationship between the meter-in throttles 10a and 10b and the center bypass throttle 11 with respect to the stroke of the directional control valve 10. As can be seen from this figure, the meter-in throttles 10a and 10b have an opening area of 0 (fully closed) in the stroke where the direction switching valve 10 is in the vicinity of neutral, and the stroke is increased when the direction switching valve 10 is operated from near neutral. Therefore, the opening area is increased, and the opening area is maximized near the maximum stroke. Center bypass throttle 11
Indicates that the opening area is maximum (full open) in the stroke where the directional control valve 10 is near neutral, and the opening area decreases as the stroke increases when the directional control valve 10 is operated from near neutral, and the opening area near the maximum stroke. Is 0 (fully closed)
become.

FIG. 3 shows a flow rate characteristic of the tilt control device 2n of the hydraulic pump 1 for controlling the negative flow rate. As can be seen from this figure, the tilt control device 2n increases the discharge flow rate of the hydraulic pump 1 according to the decrease in the pressure (negative control pressure) generated by the pressure generation device 20.

Next, the operation of the present embodiment having such a configuration will be described.

When the directional control valve 10 is in the neutral position shown in the drawing, the signal line 12b of the pressure control valve 12 is connected to the directional control valve 10.
Is in communication with the tank via a drain pipe line 14c of the pressure control valve 12 is fully opened, and pressure oil from the hydraulic pump 1 is supplied to the supply line 3, the bypass passage 4, and the center bypass throttle 11 of the direction switching valve 10. , Bypass line 13, pressure control valve 1
Then, the entire amount flows to the pressure generator 20 via 2 and the upstream pressure of the throttle 21 becomes high, and the discharge flow rate of the hydraulic pump 1 is reduced to the minimum flow rate due to the characteristics of the tilt control device 2n shown in FIG.

When the directional control valve 10 is switched from the neutral state to the left or right direction in the drawing by operating the operating lever device 30, the opening area of the center bypass throttle 11 becomes small as shown in FIG. In addition, the aperture area of the meter-in diaphragm 10a or 10b increases. When the center bypass throttle 51 is throttled in this way, the bypass flow rate is reduced, the pressure generated in the throttle 21 is reduced, and the signal line 23
The discharge flow rate of the hydraulic pump 1 is controlled to increase by the pressure detected at. When the discharge pressure of the hydraulic pump 1 becomes higher than the load pressure of the actuator 5, pressure oil starts to be supplied to the actuator 5 via the meter-in throttle of the direction switching valve 50. At the same time, the load pressure of the actuator 5 is detected by the detection path 14a or 14b and the signal line 12
It is guided to open the pressure control valve 12 via b, a control force in the valve closing direction is applied together with the spring 12s, and the outlet pressure of the center bypass throttle 11 is passed through the bypass pipe line 13 and the signal pipe line 12a. The pressure control valve 12 is guided to open, and a control force in the valve opening direction is applied, whereby the pressure control valve 12 makes the outlet pressure of the center bypass throttle 11 approximately equal to the load pressure detected by the signal line 12b. Control to be. Therefore, the front-rear differential pressure of the meter-in throttle 10a or 10b of the directional control valve 10 and the front-rear differential pressure of the center bypass throttle 11 become substantially equal, and the discharge flow rate of the hydraulic pump 1 is the meter-in throttle 10a or 1 of the directional control valve 10.
0b and the opening area ratio of the center bypass throttle 11 are divided into an inflow flow rate (meter-in flow rate) into the actuator 5 passing through the meter-in throttle 10a or 10b and a bypass flow rate passing through the center bypass throttle 11.

In such a state, when the load pressure of the actuator 5 increases, the hydraulic pump 1 responds accordingly.
Discharge pressure rises, and the pressure in the bypass pipe line 13 also rises, but the load pressure is introduced from the detection pipe 14a or 14b to the pressure control valve 12 via the signal pipe 12b, and the pressure control valve 12 is closed. Acts in the valve direction. Then, the opening area of the pressure control valve 12 decreases in accordance with the increase in the load pressure, and the bypass flow rate decreases. Therefore, the pressure generated in the throttle 21 decreases in accordance with the decrease in the flow rate. This reduced pressure is guided to the tilt control device 2n via the signal line 23, the discharge flow rate of the hydraulic pump 1 is increased by the negative flow rate control of the tilt control device 2n, and this increased discharge flow rate is switched again. The flow rate is divided into the actuator inflow flow rate and the bypass flow rate according to the opening area ratio between the meter-in throttle 10a or 10b of the valve 10 and the center bypass throttle 11. Therefore, as shown in the characteristic diagram of FIG. 4, the flow rate into the actuator 5 becomes a flow rate according to the opening area ratio between the meter-in throttle 10a or 10b and the center bypass throttle 11.
A constant inflow flow rate characteristic (metering characteristic) can be obtained regardless of the load pressure.

As a comparative example, consider a hydraulic drive system provided with a general center bypass type directional control valve without the pressure control valve 12. In such a hydraulic drive,
When the load pressure of the actuator 5 increases, the discharge pressure of the hydraulic pump 1 rises accordingly and the pressure generated in the throttle 21 also rises, and the discharge flow rate of the hydraulic pump 1 is controlled to decrease, and the directional control valve 5 Even if the stroke (opening area of the meter-in diaphragm) is constant, the flow rate supplied to the actuator 5 decreases. Therefore, the flow rate characteristic (metering characteristic) into the actuator 5 is shown in FIG.
As shown in (3), it changes according to the load pressure, a dead zone occurs on the small stroke side, and operability deteriorates.

Next, as another comparative example, consider the conventional hydraulic drive system shown in FIG. In this hydraulic drive system, since the variable throttle valve 52 is provided in the bypass pipe line 13, when the load pressure of the actuator 5 increases, the opening area of the variable throttle valve 52 is increased by the load pressure detected in the signal pipe line 53. Is controlled so that the bypass flow rate is reduced, the pressure generated at the throttle 21 is reduced, and the discharge flow rate of the hydraulic pump 1 is increased. This allows the hydraulic pump 1
The discharge pressure of the hydraulic pump 1 further increases without decreasing the discharge flow rate, and the load compensation characteristic that the same flow rate as before the load pressure increases can be supplied to the actuator 5 is obtained.

However, by providing the variable throttle valve 52 which throttles the opening area in response to the load pressure in the bypass pipe line 13 as described above, the center bypass throttle valve 5 is provided with respect to the bypass flow rate.
The idea is to add throttle resistance according to the load pressure in addition to the throttle resistance of No. 1, and in such a method, the center bypass throttle 51 is used in the entire stroke range of the directional control valve 50.
Cannot be matched, and proper load compensation cannot be performed in the stroke region where they do not match. This will be described with reference to FIG.

In FIG. 6, for example, a variable amount is provided so that a desired meter-in flow rate (supply flow rate to the actuator 5) can be obtained by the throttle amount (opening area) of the center bypass throttle 51 at one point M in the first half of the stroke of the direction switching valve 50. When the spring constant and the throttle opening amount of the throttle valve 52 are set, for example, in the small stroke region of the direction switching valve 50,
The opening area of the original center bypass diaphragm 51 is larger than that of the stroke matching point M. In other words, even if the variable throttle valve 52 is throttled as the load pressure increases, the throttle resistance is not sufficient and the dead zone disappears as in the first comparative example, but the dead zone still occurs.

On the other hand, in the stroke region larger than the stroke matching point M, since the original center bypass opening area is smaller than that of the stroke matching point M, the variable throttle valve 52 is throttled as the load pressure increases. Then, this throttling resistance becomes excessive, the bypass flow rate is excessively reduced, and the decrease of the negative control pressure becomes conspicuous. Therefore, the discharge flow rate of the hydraulic pump 1 excessively increases due to the negative control of the tilt control device 2n, and the meter-in flow rate significantly increases. When the hydraulic pump 1 is controlled in this way, the discharge flow rate of the hydraulic pump 1 saturates early and, contrary to the comparative example described above, a dead zone occurs on the maximum side of the stroke, and the effective stroke decreases, Operability is reduced.

In the stroke region larger than the matching stroke point M, the pump discharge flow rate increases more than necessary as described above, and the throttle resistance of the variable throttle valve 52 becomes excessive, so the pump discharge pressure also increases more than necessary. There is also a problem that the energy efficiency is lowered due to excessive power consumption.

Further, the hydraulic excavator is provided with a plurality of directional switching valves corresponding to a plurality of actuators, and the opening area of the center bypass throttle 51 built in the plurality of directional switching valves is different for each actuator. Various settings are made. Therefore, even at one of the matching stroke points M, if the unique throttle operation setting of the variable throttle valve 52 provided in the bypass passage 4 is set, the load intended for driving the actuator is applied to all of the plurality of directional control valves. Compensation will be difficult.

In the present embodiment, the pressure control valve 12 controls the outlet pressure of the center bypass throttle 11 to be substantially equal to the load pressure of the actuator 5, whereby the meter-in throttle 10a of the directional control valve 10 is controlled.
Alternatively, the front-rear differential pressure of 10b and the front-rear differential pressure of the center bypass throttle 11 become substantially equal. Therefore, the discharge flow rate of the hydraulic pump is always distributed to the actuator inflow flow rate and the bypass flow rate according to the opening area ratio between the meter-in throttle 10a or 10b of the direction switching valve 10 and the center bypass throttle 11. It always holds regardless of the load pressure. Therefore, when the direction switching valve 10 is operated and the meter-in throttle 10a or 1b is opened, the flow rate of the ratio corresponding to the opening area ratio is surely supplied to the actuator 5 at that time, and the pressure oil flows into the actuator 5. The stroke position at which is started is almost constant regardless of the load pressure. Further, the bypass flow rate side also has a flow rate according to the opening area ratio, the bypass flow rate does not excessively decrease even when the load pressure increases, and the discharge flow rate of the hydraulic pump 1 is prevented from saturating early. as a result,
As shown in FIG. 4, the flow-in characteristic of meter-in is almost constant without being affected by the load pressure, and a wide effective stroke is secured without a dead zone on either the small stroke side or the large stroke side of the directional control valve 10. And excellent operability can be obtained.

Further, since the pressure control valve 12 controls the outlet pressure of the center bypass throttle 11 of the direction switching valve 10 to be the same as the load pressure of the actuator 5, the opening area of the center bypass throttle 11 is equal to the actuator. Even if various settings are made for each, the same effect can be obtained using the same pressure control valve, and appropriate load compensation can be easily performed regardless of the setting of the opening area of the center bypass throttle.

The above operation of the present embodiment will be described in more detail.

The negative control flow rate control of the hydraulic pump 1 by the tilt control device 2n increases the discharge flow rate of the hydraulic pump 1 with respect to the decrease of the center bypass flow rate, and its characteristic is set in the tilt control device 2n. ing. However, in the hydraulic tilt control device 2n, the bypass flow rate is reduced by 21
Is detected by the pressure generated by the tilt control device 2 according to this pressure.
n is actuated to set the tilt amount of the hydraulic pump 1.

For example, let the discharge flow rate of the hydraulic pump 1 be Q _p ,
Q is the bypass flow rate passing through the center bypass throttle 11.
_t, the meter aperture 10a or 10b meter-in flow and Q _mi passing, the maximum delivery rate of the hydraulic pump 1 when the Q _o, the pump flow rate Q _p of a negative flow rate _{control, Q p = Q o -kQ t} (k : Constant) is set. The pump flow rate Q _p is also the sum of the meter-in flow rate Q _mi and the bypass flow rate Q _t, and Q _p = Q _mi + Q _t . Therefore, the meter-in flow rate Q _mi is obtained by subtracting the bypass flow rate Q _t from the pump flow rate Q _p .

Now, according to the invention, the bypass line 1
The pressure control valve 12 provided in No. 3 operates so that the outlet pressure of the center bypass throttle 11 (that is, the inlet pressure of the pressure control valve 12) becomes equal to the load pressure (that is, the outlet pressure of the meter-in throttle 10a or 10b). Therefore, the differential pressure across the meter-in throttle 10a or 10b and the differential pressure across the center bypass throttle 11 are respectively equal to the following Δ.
It becomes almost equal to P.

ΔP = P _s −P _L (P _s : discharge pressure of hydraulic pump 1 P _L : load pressure of actuator 5) That is, the opening area of the meter-in throttle 10A or 10b is A _mi , the opening area of the center bypass throttle 11 is the When a _t, each of the flow rate, where _{Q mi = C · a mi √ΔP} Q t = C · a t √ΔP ∴Q p = C (a mi + a t) √ΔP ··· (a), C = C _f √ (2 / ρ) C _f : Flow coefficient ρ: Oil density From negative control, Q _p = Q _o −k · CA _t √ ΔP (B) Therefore, the differential pressure ΔP across When determining the opening area a _t of the center bypass throttle 11 such that the [Delta] P _o becomes the value, (a) = (B) _{from, C (a mi + a t} ) √ΔP o = Q o -k · CA t √ΔP _o (1 + k) · C√ (ΔP _o ) · A _t = Q _o −C √ (ΔP _o ) · A _mi ∴A _t = (Q _o −C ′ A _mi ) / C ′ (1 + k) (C) Here, in the formula C ′ = C√ΔP _o (C), the opening area A of the meter-in throttle 10a or 10b corresponding to the stroke of the directional control valve 10 by substituting _mi, the opening area a _t of the center bypass throttle 11 can be uniquely computed.

Therefore, based on the above, the negative control flow rate control that can make the differential pressure across the throttle ΔP = ΔP _o at any stroke point is performed, and the meter-in flow rate and the bypass are controlled even when the load pressure changes. The so-called pressure compensation can be secured without changing the flow rate.

From the above, each flow rate with respect to the stroke is shown in FIG. 4, and the meter-in flow rate always has the same characteristics regardless of the change of the load pressure, and the operability is improved because there is no dead zone.

A second embodiment of the present invention will be described with reference to FIGS. In this embodiment, the present invention is applied to a hydraulic drive system including a pump displacement control device that controls positive flow rate. 7, the same members as those shown in FIG. 1 are designated by the same reference numerals.

In FIG. 7, the hydraulic pump 1 has a tilt control device 2 having a positive flow rate control characteristic as shown in FIG.
Therefore, the pressure generator 20 (throttle 21 and relief valve 22) of FIG. 1 related to the negative flow rate control in the first embodiment is not provided, and the shuttle valve 32 and the signal line 33 related to the positive flow rate control are not provided. Is provided,
The pilot pressure by the operating lever device 30 is taken out to the signal conduit 33 via the shuttle valve 32 and guided to the tilt control device 2p.

In the embodiment constructed as described above, the operation lever device 30 is not operated, and the directional control valve 10 is operated.
Is the signal line 1 of the pressure control valve 12 when the operation is in the neutral state shown in the figure.
2b communicates with the tank via the drain pipe 14c of the direction switching valve 10, the pressure control valve 12 is fully opened, and the pressure oil from the hydraulic pump 1 is supplied to the supply passage 3, the bypass passage 4, and the center bypass throttle. The tilt control device 2p connected to the shuttle valve 32 via the signal line 33 while there is no input to the pilot lines 31a and 31b while the entire amount flows to the tank through the bypass line 11, the bypass line 13 and the pressure control valve 12. The positive flow rate control reduces the pump discharge flow rate.

When the operation lever device 30 is operated so that the direction switching valve 10 is switched to either the right or left direction in the figure, the corresponding pilot pressure is guided to the tilt control device 2p via the shuttle valve 32 and the signal line 33. The positive flow rate control of the tilt control device 2p is performed based on the signal pressure (pilot pressure), and the discharge flow rate of the hydraulic pump 1 increases.
At the same time, the directional control valve 10 is switched and the opening area of the center bypass throttle 11 decreases according to the pilot pressure, and the opening area of the meter-in throttle 10a or 10b starts to increase. Then, the load pressure of the actuator 5 is guided to close the pressure control valve 12 via the detection path 14a or 14b and the signal conduit 12b, a control force in the valve closing direction is applied together with the spring 12s, and the center bypass is applied. The outlet pressure of the throttle 11 is guided to open the pressure control valve 12 via the bypass pipe line 13 and the signal pipe line 12a, and a control force in the valve opening direction is imparted to the pressure control valve 12 so that the center bypass throttle pipe 11 is opened. The outlet pressure is controlled so as to be substantially equal to the detected load pressure. Therefore, the discharge flow rate of the hydraulic pump 1 is divided into the flow rate into the actuator 5 and the bypass flow rate into the bypass line 13 according to the opening area ratio between the meter-in throttle 10a or 10b of the direction switching valve 10 and the center bypass throttle 11. It is distributed, and the same effect as the first embodiment is obtained.

A third embodiment of the present invention will be described with reference to FIG. In the present embodiment, the present invention is applied to a hydraulic drive system including a pump displacement control device for controlling a negative flow rate, in which the directional control valve is a multiple valve. 9, the same members as those shown in FIG. 1 are designated by the same reference numerals.

In FIG. 9, a directional control valve 10A which constitutes a multiple valve together with the directional control valve 10 is provided, and the directional control valve 10A is provided in the supply passage 3 for the discharge flow rate from the hydraulic pump 1 via the bypass conduit 40. The opening areas of the meter-in throttles 10a and 10b built in the directional control valve 10A are changed by operating the directional control valve 10A which is connected to control the flow rate of the pressure oil supplied to the actuator 5A. Further, the bypass passage 4a downstream of the center bypass throttle 11 of the directional control valve 10 is built in the directional control valve 10A so that the opening area becomes smaller as the stroke (switching amount) of the directional control valve 10A increases. An interlocking center bypass throttle 11A is provided, and a pressure control valve 12 is provided in a bypass pipe line 13 on the downstream side of the center bypass throttle 11A.

Like the direction switching valve 10, the direction switching valve 10A has a detection path 14 for guiding the load pressure of the actuator 5A.
a, 14b and a drain passage 14c are provided, and any one of the detection passages 14a, 14b and the drain passage 14c is connected to the load pressure introducing passage 17 according to the operation of the directional control valve 10A. On the other hand, in the direction switching valve 10, the direction switching valve 10
Detection paths 14a, 14b and drain path 14 depending on the operation of
Any one of c is connected to the load pressure introducing passage 16.

The load pressure introducing passages 16 and 17 are connected to the signal pipe 12b of the pressure control valve 12 via the shuttle valve 15.

The load pressures of the actuators 5 and 5A driven by the operation of the directional control valves 10 and 10A are guided to the shuttle valve 15 via the load pressure introducing passages 16 and 17, and the shuttle valve 15 controls the high pressure side of the high pressure side. A pressure (maximum load pressure) is selected, the selected load pressure is guided to the pressure control valve 12 via the signal line 12b, and the operation of the pressure control valve 12 is controlled based on the maximum load pressure. .
Therefore, when each of the actuators 5 and 5A is individually operated, load compensation by the pressure control valve 12 can be performed as in the first embodiment. Further, by providing a pressure compensating valve (pressure control valve) for keeping the differential pressure across the meter-in throttles 10a and 10b constant at the downstream side of the meter-in throttles 10a and 10b of the direction switching valves 10 and 10A, the actuators 5 and 5A are provided. In the combined operation of simultaneously driving the valves, the outlet pressure of the center bypass throttle 11A of the directional control valve 10A is controlled to be the same as the maximum load pressure, and the meter-in throttle 10a or 10b of the directional control valve relating to the actuator on the high load pressure side is controlled. The differential pressure across the center bypass throttle 11, 11A and the differential pressure upstream and downstream of the center bypass throttle 11, 11A are substantially equal to each other.
The aperture area of each meter-in aperture of A and the composite aperture area of the center bypass apertures 11 and 11A (the aperture area of the center bypass aperture 11 and the center bypass aperture 11A)
The product is divided into the inflow flow rate into a plurality of actuators and the bypass flow rate according to the ratio of the flow rate to the plurality of actuators, and the bypass flow rate. Appropriate load compensation can be performed and excellent composite operability can be obtained.

In the above embodiment, the hydraulic pump 1
Although the hydraulic type is used as the tilt control device of FIG. 1, an electronically controlled tilt control device may be used, and the same effect can be obtained.

In the above embodiment, the hydraulic pump 1 is a variable displacement type and the pump discharge flow rate is controlled by controlling the displacement of the hydraulic pump 1. However, the hydraulic pump 1 is a fixed pump and the hydraulic pump is driven. The pump discharge flow rate may be controlled by controlling the rotational speed of the engine, and the same effect can be obtained by applying the present invention to such a hydraulic drive device.

[0064]

According to the present invention, when an open center type directional control valve is operated to drive an actuator, appropriate load compensation can be performed in the entire stroke region of the directional control valve.
Excellent operability with a wide effective stroke region can be obtained, and appropriate load compensation can be easily performed regardless of the setting of the opening area of the center bypass throttle of the directional control valve.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a hydraulic drive system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an opening area and a stroke of a meter-in throttle and a center bypass throttle of a directional control valve.

FIG. 3 is a diagram showing a flow rate characteristic of a tilt control device that controls a negative flow rate.

FIG. 4 is a diagram showing meter-in flow rate characteristics, bypass flow rate characteristics, and pump flow rate characteristics.

FIG. 5 is a diagram showing a meter-in flow rate characteristic of a conventional hydraulic drive system.

FIG. 6 is a diagram showing a meter-in flow rate characteristic of another conventional hydraulic drive system.

FIG. 7 is a hydraulic circuit diagram of a hydraulic drive system according to a second embodiment of the present invention.

FIG. 8 is a diagram showing a flow rate characteristic of a tilt control device for controlling a positive flow rate.

FIG. 9 is a hydraulic circuit diagram of a hydraulic drive system according to a third embodiment of the present invention.

FIG. 10 is a hydraulic circuit diagram of a conventional hydraulic drive system.

[Explanation of symbols]

 1 Variable displacement hydraulic pump 2n Tilt control means (negative control) 2p Tilt control means (positive control) 3 Supply path 4 Bypass passage 5 Actuator 6 Safety valve 7 Check valve 10 Direction switching valve 10a, 10b Meter-in throttle 11 Center bypass Throttle 12 Pressure control valve 12a, 12b Signal line 12s Spring 12v Valve body 13 Bypass line 14a, 14b Detection line 14c Drain line 15 Shuttle valve 16 Load pressure introduction line 17 Load pressure introduction line 20 Pressure generator 21 Throttle 22 Low pressure Relief valve 23 Signal line (negative control signal line) 30 Operating lever device 31a, 31b Pilot line 32 Shuttle valve 33 Signal line (positive control signal line)

Claims (4)

[Claims] 1. An open center type having a hydraulic pump, at least one actuator driven by pressure oil discharged from the hydraulic pump, and a center bypass throttle on a bypass passage communicating the hydraulic pump and a tank. A directional control valve, and pump control means for controlling the discharge flow rate of the hydraulic pump in response to the operation of the directional control valve, and the pressure supplied from the hydraulic pump to the actuator in response to the operation of the directional control valve. In a hydraulic drive device that controls the flow rate of oil, a detection unit that detects the load pressure of the actuator, and the outlet passage of the center bypass throttle is disposed downstream of the center bypass throttle of the bypass passage in the valve opening direction. The load pressure applied and detected by the detection means is applied in the valve closing direction, and Hydraulic drive system, characterized in that it comprises a pressure control valve which is controlled to be the outlet pressure of the diaphragm equal to the load pressure of the actuator. 2. A hydraulic pump, and a plurality of actuators driven by pressure oil discharged from the hydraulic pump,
A plurality of open center type directional control valves that are connected in series to a bypass passage that communicates the hydraulic pump and the tank and each have a center bypass throttle on the bypass passage, and the directional control valves that operate according to the operation of the plurality of directional control valves. And a pump control means for controlling a discharge flow rate of the hydraulic pump, wherein the hydraulic drive apparatus controls the flow rate of the pressure oil supplied from the hydraulic pump to the plurality of actuators in accordance with the operation of the plurality of directional control valves. A detection unit that detects the maximum load pressure of the plurality of actuators, and is arranged on the downstream side of the most downstream center bypass throttle in the bypass passage, and the outlet pressure of the most downstream center bypass throttle is applied in the valve opening direction. The maximum load pressure detected by the detection means is applied in the valve closing direction, and Hydraulic drive system, characterized in that it comprises a pressure control valve which is controlled to be the outlet pressure of the diaphragm the same as the maximum load pressure. 3. The hydraulic drive system according to claim 1, wherein the hydraulic pump is of a variable displacement type, and the pump control means is arranged further downstream of the pressure control valve in the bypass passage, And a tilting control means for negatively controlling the discharge capacity of the hydraulic pump according to the pressure generated by the pressure generating device. . 4. The hydraulic drive system according to claim 1 or 2, wherein the hydraulic pump is of a variable displacement type, and the pump control means includes means for detecting an operation signal of an operation means for the directional control valve, A hydraulic drive device, which is tilting control means for controlling a positive flow rate of a discharge capacity of the hydraulic pump according to an operation signal detected by the detection means.